Cellulose (2017) 24:1759–1773
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(HRP, P8250, type II, 181 U mg - 1 ) from Sigma- Aldrich. Epoxy resin (Araldite LY 556) and amine hardener (XB 3473) were purchased from Mouldlife (Suffolk, UK). The water used for all experiments was deion- ized and further purified in a UV unit (Synergy Millipore, Molsheim, France). NaNO 3 and NaBD 4 were purchased from Aldrich and used as received.
based composites with improved mechanical and thermal stability. Furthermore, it was our aim to demonstrate a process resulting in pre- dictable nanocomposite properties. Nanocomposites were prepared by lamination of nanopapers. The production of these nanopaper laminates and their characterization are reported. Furthermore, compos- ites based on bacterial cellulose (BC) nanopapers were produced as control and compared with the CNF nanopaper composites. The reasons behind the observed effects were discussed.
Methods for CNF modification, nanopaper and composites production and testing
Hydrolysis and oxidation of GG
Experimental
Endo-1,4- b -mannanase was used to partially hydro- lyze GG. GG was dissolved in deionized water to produce a 1.0% (w/v) solution, the enzyme added and the solution incubated at 40 C in a water bath for 4 h. In order to deactivate the enzyme it was heated to 100 C for 10 min. The samples were centrifuged at 5000 rpm and the supernatant was collected and freeze-dried. Hydrolyzed GG was enzymatically oxidized (OGG) whereby the dosage of the enzymes was based on the amount of galactose present in the GG sample: 1.50 units (U) of GO, 150 U of catalase and 0.9 U of HRP per mg of galactose (Lucenius et al. 2014; Parikka et al. 2010). 1% (w/v) solutions of GG were stirred in the presence of the enzymes at ? 4 C for 72 h. Afterwards the sample was heated to 90 C while mixing in order to inactivate the enzymes.
Materials
Cellulose nanofibrils (CNF) were prepared by disinte- gration of unmodified never dried industrial bleached birch pulp. The pulp was passed six times through a high-pressure fluidizer (Microfluidics, M-110Y, Microfluidics Int. Co., Newton, USA) following a procedure described previously (O¨ sterberg et al. 2013). The CNF had diameters ranging between 5 and 100 nm but the majority of the fibrils were in the range of 5–20 nm with a few larger fibril bundles being present. The length of the fibrils was a few micrometers. No loss of mass was observed during the fibrillation process. Commercially available bacterial cellulose was kindly supplied by fzmb GmbH (Bad Langensalza, Germany) in the form of wet pellicles containing 92 wt% water. The diameter of BC was found to be approximately 50 nm with fibril lengths of up to several micrometers (Lee and Bismarck 2012). Two types of water-soluble polysaccharides (WSPS) were introduced into the CNF network. Commercial guar gum galactomannan (GG, M w [ 1000 kDa) from Sigma Aldrich (Lot#041 M 0058 V, Pcode 10011170894) was used after enzymatic modification. Spruce galactoglucomannan (GGM, Picea abies, M w 20–60 kDa) was extracted from the process water of a Finnish pulp mill in an industrial-scale isolation trial after ethanol precipitation (Xu et al. 2008). Enzymes were used to hydrolyze and oxidize GG. Endo-1,4- b - mannanase (Lot 00803, from Aspergillus niger, EC number 3.2.1.78, 42 U mg - 1 ) was purchased from Megazyme (Wicklow, Ireland), galactose oxidase (GO, G7400, 3685 U g - 1 , EC 1.1.3.9), catalase (from bovine liver, C30, 22,000 U mg - 1 ) and horseradish peroxidase
Determination of the molecular weight and the degree of oxidation of GG
The molecular weight (M w ) of GG hydrolyzed with mannanase was determined using size exclusion chromatography (SEC). M w was calculated using a dn/dc value of 0.15 mL g - 1 . The hydrolyzed GG was dissolved in 0.1 M NaNO 3 by stirring for 7 d and filtered through a 0.45 l m filter. The method is described in detail by Parikka et al. (2010). Gas chromatography mass spectrometry (GC–MS) was used to determine the degree of oxidation (DO). Briefly, the samples (1 mg of polysaccharide) were deuterium labelled with NaBD 4 , precipitated and acid methanolyzed. GO was used to selectively oxidize the galactosyl units of GG. The degree of oxidation was calculated as described in literature (Parikka et al. 2010).
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